EP0594117B1 - Piezoelectric filter and its production method - Google Patents
Piezoelectric filter and its production method Download PDFInfo
- Publication number
- EP0594117B1 EP0594117B1 EP19930116850 EP93116850A EP0594117B1 EP 0594117 B1 EP0594117 B1 EP 0594117B1 EP 19930116850 EP19930116850 EP 19930116850 EP 93116850 A EP93116850 A EP 93116850A EP 0594117 B1 EP0594117 B1 EP 0594117B1
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- Prior art keywords
- plate
- substrate
- piezoelectric
- piezoelectric filter
- holding
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- 238000004519 manufacturing process Methods 0.000 title claims description 22
- 239000000758 substrate Substances 0.000 claims description 206
- 239000011521 glass Substances 0.000 claims description 58
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 claims description 55
- 230000003534 oscillatory effect Effects 0.000 claims description 31
- 229910052710 silicon Inorganic materials 0.000 claims description 24
- 239000010703 silicon Substances 0.000 claims description 23
- WSMQKESQZFQMFW-UHFFFAOYSA-N 5-methyl-pyrazole-3-carboxylic acid Chemical compound CC1=CC(C(O)=O)=NN1 WSMQKESQZFQMFW-UHFFFAOYSA-N 0.000 claims description 20
- GQYHUHYESMUTHG-UHFFFAOYSA-N lithium niobate Chemical compound [Li+].[O-][Nb](=O)=O GQYHUHYESMUTHG-UHFFFAOYSA-N 0.000 claims description 20
- 238000000034 method Methods 0.000 claims description 18
- RIUWBIIVUYSTCN-UHFFFAOYSA-N trilithium borate Chemical compound [Li+].[Li+].[Li+].[O-]B([O-])[O-] RIUWBIIVUYSTCN-UHFFFAOYSA-N 0.000 claims description 16
- 238000010438 heat treatment Methods 0.000 claims description 14
- 150000003377 silicon compounds Chemical class 0.000 claims description 6
- 239000000463 material Substances 0.000 claims description 3
- 238000005498 polishing Methods 0.000 claims description 3
- 238000005406 washing Methods 0.000 claims 1
- 239000010453 quartz Substances 0.000 description 21
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 description 19
- 229910052681 coesite Inorganic materials 0.000 description 16
- 229910052906 cristobalite Inorganic materials 0.000 description 16
- 239000000377 silicon dioxide Substances 0.000 description 16
- 229910052682 stishovite Inorganic materials 0.000 description 16
- 229910052905 tridymite Inorganic materials 0.000 description 16
- 238000005530 etching Methods 0.000 description 11
- 230000004048 modification Effects 0.000 description 11
- 238000012986 modification Methods 0.000 description 11
- 238000000151 deposition Methods 0.000 description 8
- VYZAMTAEIAYCRO-UHFFFAOYSA-N Chromium Chemical compound [Cr] VYZAMTAEIAYCRO-UHFFFAOYSA-N 0.000 description 7
- 239000000853 adhesive Substances 0.000 description 7
- 230000001070 adhesive effect Effects 0.000 description 7
- 229910052804 chromium Inorganic materials 0.000 description 7
- 239000011651 chromium Substances 0.000 description 7
- 238000010276 construction Methods 0.000 description 7
- PCHJSUWPFVWCPO-UHFFFAOYSA-N gold Chemical compound [Au] PCHJSUWPFVWCPO-UHFFFAOYSA-N 0.000 description 7
- 229910052737 gold Inorganic materials 0.000 description 7
- 239000010931 gold Substances 0.000 description 7
- 239000007788 liquid Substances 0.000 description 7
- 238000000206 photolithography Methods 0.000 description 7
- 230000000694 effects Effects 0.000 description 5
- 238000005516 engineering process Methods 0.000 description 5
- 239000010408 film Substances 0.000 description 5
- 239000010409 thin film Substances 0.000 description 5
- XLOMVQKBTHCTTD-UHFFFAOYSA-N Zinc monoxide Chemical compound [Zn]=O XLOMVQKBTHCTTD-UHFFFAOYSA-N 0.000 description 4
- 238000005229 chemical vapour deposition Methods 0.000 description 4
- 230000008569 process Effects 0.000 description 4
- 239000012790 adhesive layer Substances 0.000 description 3
- 238000010295 mobile communication Methods 0.000 description 3
- PMHQVHHXPFUNSP-UHFFFAOYSA-M copper(1+);methylsulfanylmethane;bromide Chemical compound Br[Cu].CSC PMHQVHHXPFUNSP-UHFFFAOYSA-M 0.000 description 2
- 239000013078 crystal Substances 0.000 description 2
- 230000010358 mechanical oscillation Effects 0.000 description 2
- 230000004044 response Effects 0.000 description 2
- 238000004544 sputter deposition Methods 0.000 description 2
- 239000011787 zinc oxide Substances 0.000 description 2
- JBRZTFJDHDCESZ-UHFFFAOYSA-N AsGa Chemical compound [As]#[Ga] JBRZTFJDHDCESZ-UHFFFAOYSA-N 0.000 description 1
- WHXSMMKQMYFTQS-UHFFFAOYSA-N Lithium Chemical compound [Li] WHXSMMKQMYFTQS-UHFFFAOYSA-N 0.000 description 1
- 230000008859 change Effects 0.000 description 1
- 230000008878 coupling Effects 0.000 description 1
- 238000010168 coupling process Methods 0.000 description 1
- 238000005859 coupling reaction Methods 0.000 description 1
- 238000011161 development Methods 0.000 description 1
- 238000003780 insertion Methods 0.000 description 1
- 230000037431 insertion Effects 0.000 description 1
- 229910052744 lithium Inorganic materials 0.000 description 1
- 230000010355 oscillation Effects 0.000 description 1
- 230000010287 polarization Effects 0.000 description 1
- 239000004065 semiconductor Substances 0.000 description 1
- 239000000126 substance Substances 0.000 description 1
- 229910021489 α-quartz Inorganic materials 0.000 description 1
Images
Classifications
-
- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
- H03H9/00—Networks comprising electromechanical or electro-acoustic devices; Electromechanical resonators
- H03H9/46—Filters
- H03H9/54—Filters comprising resonators of piezoelectric or electrostrictive material
- H03H9/56—Monolithic crystal filters
- H03H9/562—Monolithic crystal filters comprising a ceramic piezoelectric layer
-
- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
- H03H3/00—Apparatus or processes specially adapted for the manufacture of impedance networks, resonating circuits, resonators
- H03H3/007—Apparatus or processes specially adapted for the manufacture of impedance networks, resonating circuits, resonators for the manufacture of electromechanical resonators or networks
- H03H3/02—Apparatus or processes specially adapted for the manufacture of impedance networks, resonating circuits, resonators for the manufacture of electromechanical resonators or networks for the manufacture of piezoelectric or electrostrictive resonators or networks
-
- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
- H03H9/00—Networks comprising electromechanical or electro-acoustic devices; Electromechanical resonators
- H03H9/46—Filters
- H03H9/54—Filters comprising resonators of piezoelectric or electrostrictive material
- H03H9/56—Monolithic crystal filters
- H03H9/564—Monolithic crystal filters implemented with thin-film techniques
Definitions
- the present invention relates to a piezoelectric filter utilizing piezoelectric property of an oscillatory piezoelectric plate made of lithium tantalate, lithium niobate or lithium borate.
- the piezoelectric filter has such a basic construction as shown in Fig. 22 and includes an oscillatory piezoelectric plate 1501, a pair of upper electrodes 1502 formed on an upper face of the piezoelectric plate 1501 and a lower electrode 1503 formed on a lower face of the piezoelectric plate 1501.
- the upper electrodes 1502 and the lower electrode 1503 on the single piezoelectric plate 1501 form two sets of counter electrodes.
- This known piezoelectric filter is a double mode monolithic piezoelectric filter based on a principle in which electric signals are converted into mechanical oscillations by one set of the counter electrodes and the mechanical oscillations are converted into the electric signals by the other set of the counter electrodes.
- Bandwidth obtained in such a filter depends upon piezoelectric constant of the piezoelectric plate 1501 and is about 0.2 % of that at a central frequency in fundamental mode when an AT-CUT quartz plate in ordinary use is employed. In the case of higher-order mode, i.e. overtone of n-th order, bandwidth is further narrowed to 1/(n 2 ) of 0.2 %.
- first intermediate frequency is raised to about 200 MHz by widening of the channel bands.
- the elastic surface wave filter since overtone of higher order is employed, it is difficult to obtain a broad band. Consequently, generally, the elastic surface wave filter has been used for the broad-band first intermediate frequency filter.
- the elastic surface wave filter is neither satisfactory in both shape and weight nor is electrically sufficient due to insertion loss, etc.
- the quartz plate should be made thin because the resonance frequency is inversely proportional to thickness of the quartz plate.
- the quartz plate When the AT-CUT quartz plate in ordinary use is oscillated at, for example, 100 MHz, the quartz plate should have a thickness of about 17 ⁇ m and thus, production of the quartz plate is extremely difficult. Furthermore, even if such a quartz plate is produced satisfactorily, handling for mounting the quartz plate and connection of the quartz plate to an external circuit are quite difficult due to small thickness of the quartz plate.
- a method is also proposed by Japanese Patent Laid-Open Publication No. 3-235408 (1991) in which quartz of an oscillatory portion is made thin by etching so as to be capable of being used at high frequency.
- quartz of an oscillatory portion is made thin by etching so as to be capable of being used at high frequency.
- this known method only the oscillatory portion of the quartz plate having a thickness of about 70 ⁇ m is made thin to about 20 ⁇ m by etching such that high-frequency oscillation of the oscillatory portion is made possible. Since resonance frequency is controlled by etching, it will be extremely difficult due partly to etching accuracy to mass produce filters in which bandwidth is quite narrow and accuracy of central frequency is strict.
- electromechanical coupling coefficient of the piezoelectric substrate may be changed to a larger one. Nevertheless, since there is not much difference of velocity of sound therebetween, problem of thickness control is not solved yet.
- a piezoelectric filter at high high frequency is disclosed in, for example, a paper entitled “Film Bulk Acoustic wave Resonator Technology” in 1990 Ultrasonic Symposium Proceedings, page 529 and U.S. Patent No. 4719383 entitled “Piezoelectric Shear Wave Resonator and Method of Making Same".
- a cushioning film 2102 of SiO 2 is formed on a substrate 2101 of silicon or gallium-arsenic as shown in Fig. 23.
- electrodes 2104 and 2105 are formed. As a result, a resonator or a filter is obtained.
- the piezoelectric member in this technology, zinc oxide or aluminum nitride is used for the piezoelectric member.
- This piezoelectric member can be advantageously formed by sputtering, i.e. thin film forming technology.
- the piezoelectric member is made of polycrystalline material, crystals should be aligned in C-axis in order to obtain piezoelectric property. Undesirably, this alignment largely depends upon thin film forming conditions or devices and changes according to thickness of the film deposited on the substrate or material of the ground.
- quartz, lithium niobate, lithium tantalate, lithium borate or the like in polycrystalline form does not exhibit sufficient piezoelectric property.
- quartz is widely used for an oscillator, a filter or the like due to its high stability and excellent temperature characteristics but only ⁇ quartz which is monocrystalline and has a crystalline structure symmetric with respect to a threefold axis exhibits piezoelectric property.
- the substrate acts as the piezoelectric member and its central frequency is set to 100 MHz
- the substrate has a thickness of 17 ⁇ m.
- the piezoelectric member should have an accuracy of not more than 1 ⁇ m. Since error of thickness of the adhesive layer directly determines accuracy of frequency, it is considered impossible to attain such an accuracy of the piezoelectric member in this method and the arrangement.
- Document EP 503, 892 discloses a high frequency filter formed by directly bonding a quartz crystal resonator to a semiconductor substrate.
- an essential object of the present invention is to provide a piezoelectric filter which can be used also in a superhigh frequency band and can be mass produced.
- a method of producing a piezoelectric substrate comprises the steps of directly bonding a piezoelectric substrate to a substrate for holding the piezoelectric substrate, the piezoelectric substrate acting as an oscillator and being made of one of lithium tantalate, lithium niobate and lithium borate, while the substrate is made of one of quartz, lithium tantalate, lithium niobate and lithium borate, and mechanically polishing the piezoelectric substrate and the substrate so as to adjust a thickness of the piezoelectric substrate and the substrate. Since the piezoelectric substrate and the substrate are directly bonded to each other, the piezoelectric filter has remarkably high geometric precision by sufficiently controlling the thickness of the piezoelectric substrate and the substrate and flatness of the piezoelectric substrate and the substrate.
- the piezoelectric filter K1 includes an oscillatory substrate 101 acting as a piezoelectric substrate, a glass substrate 102 for holding the substrate 101, an input electrode 103, an output electrode 104 and an earth electrode 105.
- the substrate 101 is bonded to the glass substrate 102 by direct bonding.
- the input and output electrodes 103 and 104 are provided on upper faces of the substrate 101 and the glass substrate 102, while the earth electrode 105 is provided on lower faces of the substrate 101 and the glass substrate 102.
- the glass substrate 102 is formed with a recess R, while the substrate 101 has an oscillatory portion P confronting the recess R.
- the earth electrode 105 may also be divided into a plurality of, for example, a pair of earth electrodes 105a.
- the piezoelectric substrate but may be formed from any one of lithium tantalate, lithium niobate and lithium borate.
- Fig. 4 shows production steps of the piezoelectric filter K1.
- the substrate 101 and the glass substrate 102 are initially polished and washed. Then, the substrate 101 and the glass substrate 102 are subjected to a hydrophilic treatment by using hydrophilic liquid so as to be bonded to each other by direct bonding. At this time, the substrate 101 and the glass substrate 102 are already bonded to each other. However, since this bonding strength is quite small, the substrate 101 and the glass substrate 102 can be neither secured to each other nor processed.
- the substrate 101 and the glass substrate 102 are heat treated at a predetermined temperature which should be lower than a temperature leading to loss of piezoelectric property of the piezoelectric substrate 101 and a softening point of the glass substrate 102.
- Lithium tantalate loses piezoelectric property at a temperature of about 600 °C
- lithium niobate loses piezoelectric property at a temperature of about 1000 °C
- lithium borate loses piezoelectric property at a temperature of about 600 °C.
- glass used for the glass substrate 102 has a softening point of 450 °C.
- the predetermined temperature is set at 300 °C.
- the substrate 101 and the glass substrate 102 are securely bonded to each other without using adhesive. Then, the substrate 101 is polished so as to adjust its thickness. Subsequently, in order to produce the oscillatory portion P of the substrate 101, a portion of the glass substrate 102, which confronts the oscillatory portion P, is removed by etching and thus, the recess R is obtained. Then, the signal electrodes 103 and 104 and the earth electrode 105 are produced by depositing chromium and gold, respectively and photolithography.
- Fig. 5 shows production steps of a piezoelectric filter K1' which is a first modification of the piezoelectric filter K1.
- the piezoelectric filter K1' includes a glass substrate 102' which is made of glass having a coefficient of thermal expansion substantially identical with that of the substrate 101. Since other constructions of the piezoelectric filter K1' are similar to those of the piezoelectric filter K1, the description is abbreviated for the sake of brevity.
- the substrate 101 and the glass substrate 102' are initially polished and washed. Then, the substrate 101 and the glass substrate 102' are subjected to a hydrophilic treatment by using hydrophilic liquid so as to be bonded to each other by direct bonding. At this time, the substrate 101 and the glass substrate 102' are already bonded to each other. However, since this bonding strength is quite small, the substrate 101 and the glass substrate 102' can neither be secured to each other nor processed. Thus, in order to increase the bonding strength, the substrate 101 and the glass substrate 102' are heat treated at a temperature of 450 °C. The bonding strength is determined by this heat treatment temperature. As the heat treatment temperature is raised, the bonding strength increases.
- permissible heat treatment temperature is determined by coefficients of thermal expansion of the piezoelectric substrate 101 and glass of the glass substrate 102' and thicknesses of the substrate 101 and the glass substrate 102'.
- the heat treatment temperature can be raised further as the above coefficients of thermal expansion become smaller and thickness of the substrate 101 becomes smaller relative to that of the glass substrate 102'.
- the substrate 101 and the glass substrate 102' are securely bonded to each other without using adhesive.
- the substrate 101 is polished. Since the heat treatment has been performed at 450 °C, bonding strength between the substrate 101 and the glass substrate 102' is quite large. As a result, the substrate 101 can be polished to a thickness of 8 ⁇ m.
- the signal electrodes 103 and 104 and the earth electrode 105 are produced by depositing chromium and gold, respectively and photolithography.
- the piezoelectric filter K1' produced as described above has characteristics shown in Fig. 6. As shown in Fig. 6, the piezoelectric filter K1' has a central frequency of 200 MHz, which has been so far difficult to obtain in a known method of producing a piezoelectric filter.
- Fig. 7 shows a piezoelectric filter K1'' which is a second modification of the piezoelectric filter K1.
- the glass substrate 102 of the piezoelectric filter K1 is replaced by a silicon substrate 102". Since other constructions of the piezoelectric filter K1'' are similar to those of the piezoelectric filter K1, the description is abbreviated for the sake of brevity.
- the piezoelectric substrate K1'' of the above described arrangement has characteristics shown in Fig. 8. As shown in Fig. 8, the piezoelectric filter K1'' has a central frequency of 100 MHz, which has been so far difficult to obtain in a known piezoelectric filter.
- Fig. 9 shows production steps of the piezoelectric filter K1".
- the substrate 101 and the silicon substrate 102" are initially polished and washed. Then, the substrate 101 and the silicon substrate 102" are subjected to a hydrophilic treatment by using hydrophilic liquid so as to be bonded to each other by direct bonding. At this time, the substrate 101 and the silicon substrate 102" are already bonded to each other. However, since this bonding strength is quite small, the substrate 101 and the silicon substrate 102'' can be neither secured to each other nor processed. Thus, in order to increase the bonding strength, the substrate 101 and the silicon substrate 102" are heat treated at a predetermined temperature which should be lower than a temperature leading to loss of piezoelectric property of the piezoelectric substrate 101.
- Lithium tantalate loses piezoelectric property at a temperature of about 600 °C
- lithium niobate loses piezoelectric property at a temperature of about 1000 °C
- lithium borate loses piezoelectric property at a temperature of about 600 °C
- the predetermined temperature is set at 300 °C.
- Fig. 10 shows a piezoelectric filter K1"' which is a third modification of the piezoelectric filter K1.
- the substrate 101 acting as a piezoelectric substrate and the substrate 102 for holding the substrate 101 in the piezoelectric filter K1 are, respectively, formed by a substrate 101' made of lithium niobate and a substrate 102"' made of lithium tantalate. Since other constructions of the piezoelectric filter K1''' are similar to those of the piezoelectric filter K1, the description is abbreviated for the sake of brevity.
- the piezoelectric filter K1''' of the above described arrangement has characteristics shown in Fig. 11. As shown in Fig. 11, the piezoelectric filter K1''' has a central frequency of 100 MHz, which has been so far difficult to obtain in a known piezoelectric filter.
- Fig. 12 shows production steps of the piezoelectric filter K1"'.
- the substrates 101' and 102"' are initially polished and washed. Then, the substrates 101' and 102"' are subjected to a hydrophilic treatment by using hydrophilic liquid so as to be bonded to each other by direct bonding. At this time, the substrates 101' and 102"' are already bonded to each other. However, since this bonding strength is quite small, the substrates 101' and 102"' can be neither secured to each other nor processed. Thus, in order to increase the bonding strength, the substrates 101' and 102''' are heat treated at a predetermined temperature which should be lower than a temperature leading to loss of piezoelectric property of the piezoelectric substrate 101'.
- Lithium tantalate loses piezoelectric property at a temperature of about 600 °C
- lithium niobate loses piezoelectric property at a temperature of about 1000 °C
- lithium borate loses piezoelectric property at a temperature of about 600 °C.
- the predetermined temperature is set at 300 °C.
- Fig. 13 shows a piezoelectric filter K2 according to a second embodiment of the present invention.
- the substrate 101 and the glass substrate 102 for holding the glass substrate 101 are directly bonded to each other by SiO 2 110 formed on the glass substrate 102. Since other constructions of the piezoelectric filter K2 are similar to those of the piezoelectric filter K1, the description is abbreviated for the sake of brevity.
- the piezoelectric filter K2 of the above described arrangement has characteristics shown in Fig. 14. As shown in Fig. 14, the piezoelectric filter K2 has a central frequency of 100 MHz, which has been so far difficult to Fig. 15 shows production steps of the piezoelectric filter K2. Initially, the substrate 101 and the glass substrate 102 are polished and washed. Then, SiO 2 110 is formed on the glass substrate 102 to a thickness of 1 ⁇ m by using CVD method. Then, the substrate 101 and SiO 2 110 on the glass substrate 102 are subjected to a hydrophilic treatment by using hydrophilic liquid so as to be bonded to each other by direct bonding. At this time, the substrate 101 and the glass substrate 102 are already bonded to each other.
- the quartz substrate 101 and the glass substrate 102 are heat treated at a predetermined temperature which should be lower than a temperature leading to loss of piezoelectric property of the piezoelectric substrate 101 and a softening point of the glass substrate 102.
- Lithium tantalate loses piezoelectric property at a temperature of about 600 °C
- lithium niobate loses piezoelectric property at a temperature of about 1000 °C
- lithium borate loses piezoelectric property at a temperature of about 600 °C.
- glass used for the glass substrate 102 has a softening point of 450 °C.
- the predetermined temperature is set at 300 °C.
- SiO 2 110 is formed as a thin film and thus, is softer than glass of the glass substrate 102 and the substrate 101. Hence, even if minute foreign matter is present at the direct bonding interface between the substrate 101 and the glass substrate 102, SiO 2 110 absorbs the foreign matter, so that direct bonding between the quartz substrate 101 and the glass substrate 102 is facilitated advantageously. On the contrary, if SiO 2 is not provided at the direct bonding interface, such a case may happen that the substrate 101 and the glass substrate 102 cannot be directly bonded to each other due to minute foreign matter present at the bonding interface.
- the substrate 101 and the glass substrate 102 can be directly bonded to each other even if minute foreign matter exists at the direct bonding interface. As a result, such an effect can be achieved that yield is raised with substantially no change of electrical characteristics.
- the piezoelectric substrate is made of any one of lithium niobate, lithium tantalate and lithium borate.
- the substrate for holding is made of glass.
- the substrate for holding the substrate (101) is made of any one of silicon, lithium niobate, lithium tantalate and lithium, the same result can be obtained.
- SiO 2 is employed as silicon compound present at the direct bonding interface between the quartz substrate and the glass substrate.
- SiO 2 is replaced by Si or SiN, the same result can be obtained by achieving effects identical with those of SiO 2 .
- CVD method is employed for producing SiO 2 but may be replaced by any other method of formulating a similar film, for example, sputtering method, deposition method, etc.
- silicon compound is formed on the glass substrate but may be formed on the piezoelectric substrate so as to achieve the same effects.
- Fig. 16 shows a piezoelectric filter K2' which is a first modification of the piezoelectric filter K2.
- the glass substrate 102 of the piezoelectric filter K2 is replaced by the silicon substrate 102". Since other constructions of the piezoelectric filter K2' is similar to those of the piezoelectric filter K2, the description is abbreviated for the sake of brevity.
- the piezoelectric filter K2' of the above described arrangement has characteristics shown in Fig. 17. As shown in Fig. 17, the piezoelectric filter K2' has a central frequency of 100 MHz, which has been so far difficult to obtain in a known piezoelectric filter.
- Fig. 18 shows production steps of the piezoelectric filter K2'.
- the substrate 101 and the silicon substrate 102" are initially polished and washed.
- SiO 2 110 is formed on the silicon substrate 102" to a thickness of 1 ⁇ m by using CVD method.
- the substrate 101 and SiO 2 110 on the silicon substrate 102" are subjected to a hydrophilic treatment by using hydrophilic liquid so as to be bonded to each other by direct bonding.
- the substrate 101 and the silicon substrate 102" are already bonded to each other.
- this bonding strength is quite small, the substrate 101 and the silicon substrate 102" can be neither secured to each other nor processed.
- the substrate 101 and the silicon substrate 102" are heat treated at a predetermined temperature which should be lower than a temperature leading to loss of piezoelectric property of the piezoelectric substrate 101.
- Lithium tantalate loses piezoelectric property at a temperature of about 600 °C
- lithium niobate loses piezoelectric property at a temperature of about 1000 °C
- lithium borate loses piezoelectric property at a temperature of about 600 °C.
- the predetermined temperature is set at 300 °C.
- the signal electrodes 103 and 104 and the earth electrode 105 are produced by depositing chromium and gold, respectively and photolithography.
- Fig. 19 shows a piezoelectric filter K2'' which is a second modification of the piezoelectric filter K2.
- the substrate 101 and the substrate 102 of the piezoelectric filter K2 are formed by the substrate 101' made of lithium niobate and the substrate 102"' made of lithium tantalate, respectively. Since other constructions of the piezoelectric filter K2'' are similar to those of the piezoelectric filter K2, the description is abbreviated for the sake of brevity.
- the piezoelectric filter K2'' has characteristics shown in Fig. 20. As shown in Fig. 20, the piezoelectric filter K2'' has a central frequency of 100 MHz, which has been so far difficult to obtain in a known piezoelectric device.
- Fig. 21 shows production steps of the piezoelectric filter K2".
- the substrates 101' and 102''' are initially polished and washed.
- SiO 2 110 is formed on the substrate 102"' to a thickness of 1 ⁇ m by using CVD method.
- the substrate 101' and SiO 2 110 on the substrate 102"' are subjected to a hydrophilic treatment by using hydrophilic liquid so as to be bonded to each other by direct bonding.
- the substrates 101' and 102"' are already bonded to each other.
- this bonding strength is quite small, the substrates 101' and 102"' can be neither secured to each other nor processed.
- the substrates 101' and 102"' are heat treated at a predetermined temperature which should be lower than a temperature leading to loss of piezoelectric property of the piezoelectric substrate 101'.
- Lithium tantalate loses piezoelectric property at a temperature of about 600 °C
- lithium niobate loses piezoelectric property at a temperature of about 1000 °C
- lithium borate loses piezoelectric property at a temperature of about 600 °C.
- the predetermined temperature is set at 300 °C.
- the signal electrodes 103 and 104 and the earth electrode 105 are produced by depositing chromium and gold, respectively and photolithography.
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- Manufacturing & Machinery (AREA)
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Description
Claims (8)
- A method for manufacturing a piezoelectric filter,
comprising the steps of:a) subjecting surfaces of an oscillatory plate (101) and a substrate plate (102; 102") for holding the plate (101) to a hydrophilic treatment; the plate (101) being made of one of lithium tantalate, lithium niobate and lithium borate; the substrate plate (102; 102") for holding the plate (101) being made of one of quartz (SiO2), lithium tantalate, lithium niobate and lithium borate, glass or silicon;b) bringing the surfaces of the plate (101) and the substrate plate (102; 102") for holding the plate (101) into contact with each other; andc) subjecting the plate (101) and the substrate plate (102; 102") for holding the plate (101) to a heat treatment at a predetermined temperature such that the piezoelectric plate (101) and the substrate plate (102; 102") for holding the piezoelectric plate (101) are directly bonded to each other; the predetermined temperature being lower than a temperature leading to a loss of the piezoelectric property by the plate (101) even after the heat treatment. - The method of producing a piezoelectric filter according to claim 1, characterized in that the method contains the additional step ofa') providing silicon or silicon compound (110) on one of the opposed surfaces of said oscillatory plate (101) and said plate for holding the plate (101) prior to step a).
- The method of producing a piezoelectric filter according to one of claims 1 and 2,
characterized by the step ofd) polishing and washing said oscillatory plate (101) and said plate for holding the plate (101) at an initial stage. - A method for manufacturing a piezoelectric filter according to one of claims 1 to 3,
characterized in that said plate (101) is a piezoelectric plate. - A piezoelectric filter comprising:a) an oscillatory plate (101) which has an oscillatory portion;b) a substrate plate (102; 102") for holding the plate (101), to which the plate (101) is bonded; andc) first and second oscillatory electrode members (103, 104, 105) which are provided on opposite faces of the oscillatory portion, respectively, such that at least one of the first and second oscillatory electrode members (103, 104, 105) is divided into a plurality of counter electrodes;d) said oscillatory plate (101) is made of lithium tantalate, lithium niobate or lithium borate;e) said substrate plate (102; 102") for holding the plate (101) is made of lithium tantalate, lithium niobate, lithium borate, glass or silicon; andf) said oscillatory plate (101) is directly bonded to said substrate plate (102; 102") for holding the plate (101) according to the method of one of claims 1 to 3.
- A piezoelectric filter as claimed in claim 5,
wherein the substrate plate (102; 102") for holding the plate (101) is a glass plate (102) made of glass having a coefficient of thermal expansion substantially identical with that of material of the plate (101). - A piezoelectric filter according to claim 5 or 6,
characterized in that there is a very thin layer of silicon or silicon compound (110) between the plate (101) and said substrate plate (102; 102") for holding the plate (101). - A piezoelectric filter according to one of claims 5 to 7,
characterized in that said plate (101) is a piezoelectric plate.
Applications Claiming Priority (4)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
JP281474/92 | 1992-10-20 | ||
JP28147492 | 1992-10-20 | ||
JP281473/92 | 1992-10-20 | ||
JP28147392 | 1992-10-20 |
Publications (2)
Publication Number | Publication Date |
---|---|
EP0594117A1 EP0594117A1 (en) | 1994-04-27 |
EP0594117B1 true EP0594117B1 (en) | 1998-12-09 |
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Application Number | Title | Priority Date | Filing Date |
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EP19930116850 Expired - Lifetime EP0594117B1 (en) | 1992-10-20 | 1993-10-19 | Piezoelectric filter and its production method |
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EP (1) | EP0594117B1 (en) |
DE (1) | DE69322480T2 (en) |
Families Citing this family (2)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
EP0742598B1 (en) * | 1995-05-08 | 2000-08-02 | Matsushita Electric Industrial Co., Ltd. | Method of manufacturing a composite substrate and a piezoelectric device using the substrate |
US5759753A (en) * | 1995-07-19 | 1998-06-02 | Matsushita Electric Industrial Co., Ltd. | Piezoelectric device and method of manufacturing the same |
Family Cites Families (2)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
JPS5478693A (en) * | 1977-12-05 | 1979-06-22 | Matsushima Kogyo Co Ltd | Crystal vibrator |
JP2643620B2 (en) * | 1991-03-13 | 1997-08-20 | 松下電器産業株式会社 | Voltage controlled oscillator and method of manufacturing the same |
-
1993
- 1993-10-19 DE DE1993622480 patent/DE69322480T2/en not_active Expired - Fee Related
- 1993-10-19 EP EP19930116850 patent/EP0594117B1/en not_active Expired - Lifetime
Also Published As
Publication number | Publication date |
---|---|
EP0594117A1 (en) | 1994-04-27 |
DE69322480D1 (en) | 1999-01-21 |
DE69322480T2 (en) | 1999-08-05 |
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